(1) Field of the Invention
The invention relates to an anti-infective spacer for osteosynthesis plates comprising a plate having at least one recess for accommodating a screw, as well as a set comprising at least one osteosynthesis plate and at least one said spacer.
The term, osteosynthesis, is understood to refer to operative management of broken bones with implants, whereby implants made of biocompatible metal alloys are used most frequently. The aim of osteosynthesis is to mechanically fix reduced bone fragments during the healing phase. Said fixation enables the restoration of axis angles and articular positions of fractured bones.
Aside from nails, screws, Kirschner wires, osteosynthesis plates are used particularly frequently for osteosynthesis. Osteosynthesis plates are perforated plates made of biocompatible metal alloys. The openings in osteosynthesis plates are circular or oval in shape. Osteosynthesis plates are screwed to the ends of the fractured bones after these are reduced. The openings of the osteosynthesis plates are designed such that screw heads can be sunk, at least partially, into them. In this context, at least parts of the osteosynthesis plates contact the bone directly.
Osteosynthesis plates are usually screwed to both ends of the bone fragments using bicortical screws. However, the two-dimensional contact of osteosynthesis plates with the bone is a problem in that the contact pressure may cause necrosis of the periosteum (bone membrane) to become manifest. This was the rationale underlying the development of so-called “limited contact plates” (LCP). These osteosynthesis plates contact the periosteum only in spots or stripes. This means that the size of the contact surface of the osteosynthesis plates is reduced. Later on, so-called “dynamic compression plates” (DCP) and/or “limited contact dynamic compression plates” (LC-DCP) were developed. Said plates contain oval openings. Using screws with oval screw heads allows the screws to be tightened while concurrent compression of the bone fragments against each other is attained. Currently, so-called osteosynthesis plates with “angular stability” are available as well. Made of specialised metal alloys, these plates have a thread arranged right below the screw heads such that the screws are galled to the plate when the screws are tightened on the osteosynthesis plates. The osteosynthesis plate and the screws thus form a unit and a very stable mechanical connection is formed.
(2) Description of Related Art
Depots for local release of antimicrobial active substances have been known for decades. Accordingly, EP 0 170 979 A2 describes a depot based on gelatine. EP 0 087 662 A1 discloses an active substance depot that utilises tricalcium phosphate as carrier. Polymethylmethacrylate as carrier material for antimicrobial active substances is known from documents DE 28 15 934 A1, U.S. Pat. No. 4,191,743, and U.S. Pat. No. 4,191,740. Polymethylmethacrylate as a carrier of active substances has been introduced by Heraeus Medical and by Biomet as “Heraeus PMMA-Kette mit Gentamicin” (PMMA chain with gentamicin) and Septopal®, respectively.
A generic spacer for a bone plate is known from EP 2 005 978 B1 and comprises a coating containing a therapeutic agent, a polymer carrier, and a buffer medium. The coating is to induce bone healing and bone formation.
It is a disadvantage of known spacers that they do not have an antimicrobial effect. Moreover, the duration of the effect of the coating is limited and can be controlled only to a degree. It would also be desirable to have a simple manufacturing process, in which no additional manufacturing steps are required in order to fabricate the spacer. There is always a need for inexpensive fabrication.